ASTR 1000 Lecture Notes - Lecture 4: Greenwich Mean Time, Lunar Month, Sidereal Time
Document Summary
Sidereal day: earth rotates once on its axis in 23 hours, 56 minutes, and 4. 07 seconds. Solar day: the sun makes one circuit around the sky in 24 hours. A solar day is longer than a sidereal day by about 1/360 because earth moves about 1 in orbit each day. Sidereal month: moon orbits earth in 27. 3 days. Earth and moon travel 30 around sun during that ime (30 /360 = 1/12). Synodic month: a cycle of lunar phases; takes about 29. 5 days, 1/12 longer than a sidereal month. Sidereal year: time for earth to complete one orbit of sun. Tropical year: time for earth to complete one cycle of seasons. Tropical year is about 20 minutes (1/26,000) shorter than a sidereal year because of precession. Apparent solar ime depends on the posiion of the sun in the local sky. Mean solar ime is based on the average length of a day.
